Conventionally, aluminum or an aluminum alloy has been generally used as a wiring material for display devices such as a flat panel display. However, as the display is increased in size and improved in resolution, such a wiring comprised mainly of aluminum causes a problem of signal delay due to the properties of aluminum including high wiring resistance, making it difficult to achieve uniform image display. For this reason, studies are being made on the employment of a wiring comprised mainly of copper which is a material having a lower resistance than aluminum.
Copper has an advantage in that the resistance is low; however, copper also has problems in that when used in a gate wiring, the adhesion of copper to a substrate, such as glass, is not satisfactory, and in that when used in a source-drain wiring, diffusion of copper into the underlying silicon semiconductor film is likely to occur. For preventing the problems, studies are made on stacking a barrier film of a metal on copper, wherein the metal has both high adhesion to a substrate, such as glass, and barrier properties that diffusion of the metal into a silicon semiconductor film is unlikely to occur. As a metal for the barrier film, metals including molybdenum and titanium are studied, and a multilayer thin film structure comprising copper and the above metal or an alloy of the metal is employed.
A wiring comprised mainly of copper is formed in the form of a thin film on a substrate, such as glass, by a deposition process, such as a sputtering method, and then subjected to etching step in which the film is etched using, e.g., a resist as a mask, forming a wiring pattern. The etching step is classified into a wet etching method using an etching solution and a dry etching method using an etching gas, such as plasma.
As an etching solution for copper, an etching solution containing copper(II) ions and halide ions has been known. Such an etching solution has problems in that halide ions cause the apparatus to suffer corrosion, and in that the etching rate is too high to control the wiring form.
As an etching solution for copper or a multilayer film comprising copper, an alkaline etching solution containing copper(II) ions and ammonia has been known (see, for example, patent document 1 and non-patent documents 1 and 2). Such an etching solution containing ammonia poses problems in that, when ammonia is emitted from the etching solution, the reduction of the ammonia concentration in the etching solution causes changes of the etching rate or the odor of emitted ammonia causes the working environment to be worse. For this reason, an etching solution using, instead of ammonia, an amine having low emission properties, such as an alkanolamine, (see, for example, patent document 2) and an etching solution using an azole (see, for example, patent document 3) have also been known.
Further, as an etching solution for copper, an acidic etching solution containing hydrogen peroxide also has been known (see, for example, patent document 4). Furthermore, an acidic etching solution containing a persulfate instead of hydrogen peroxide has been known (see, for example, patent document 5). These solutions have a danger that when hydrogen peroxide or a persulfate causes a vigorous decomposition reaction, gas or heat is generated and causes breakage of the apparatus.